A new method for semiquantitative measurement of fibrin monomer complexes in plasma has been developed in our laboratory. The method is based upon the ability of fibrin monomer complexes to adhere to an immune precipitate of fibrinogen. The method is sensitive to as little as 10 micron gm/ml of fibrin monomer, it is not sensitive to plasmin digestion products of fibrinogen and is relatively insensitive to plasmin digestion products of fibrin. The method requires 0.6 ml of plasma and is done with the use of reagents that can be stored at refrigerated temperature. Further studies are needed to determine the nature of the fibrin monomer complexes which adhere to the immune precipitate and to compare the sensitivity and specificity of the new method for measuring fibrin monomer complexes with currently available methods. The studies will be done by generating various fibrin monomer complexes in vitro and determining the relative effectiveness of the new method in comparison to other methods for detecting these complexes. Additional studies comparing the new method to other methods of measuring fibrin monomer complexes in the plasma of patients with disseminated intravascular coagulation and venous thrombosis will be done. The possible mechanisms whereby fibrin monomer complexes might adhere to endothelial cell surfaces will also be examined in an in vitro system with the use of endothelial cells cultured from umbilical veins.